3 ms·Can a thing with no mass ever go less than the speed of light? Does it have a concept of time?by OneEyedRobot 5y agoCan a thing with no mass ever go less than the speed of light? Does it have a concept of time?jandrese 5y agoSure, light is slowed down when it travels through different substances. That's why we have refraction.micw 5y agoIs it really slowed down? I always assumed that it just need to take a longer way through matter than through vacuum.